Open Child Window in MVVM environment

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel;

namespace WindowWithMVVM.ViewModel
{
    public class HomeViewModel : INotifyPropertyChanged
    {
        public HomeViewModel()
        {
        }
        private string _UserInput;
        public string UserInput
        {
            get
            {
                return this._UserInput;
            }
            set
            {
                if (this._UserInput != value)
                {
                    this._UserInput = value;
                    this.NotifyPropertyChanged("UserInput");
                }
            }
        }

        protected void NotifyPropertyChanged(string property)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(property));
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}